Diamond cut-off wheel



Dec. 16, 1958 c. w. ANDERSON Re. 24,

DIAMOND CUT-OFF WHEEL Original Filed Aug. 27, 1956 2 Sheets-Sheet 1' s-,3 Y ,4 l2

Cums/we WAwnnvsan r mi? Dec. 16, 1958 c. w. ANDERSON DIAMOND CUT-OFFWHEEL 2 Sheets-Sheet 2 Original Filed Aug. 27, 1956 'NVENTOR 52 CLARENCEW. Am rrzsmv United States Patent'Ot 24,576 DIAMOND CUT-OFF WHEELClarence W. Anderson, Holden, Mass., assignor to Norton Company,Worcester, Mass., a corporation of Massachusetts Original No. 2,796,706,dated June 25, 1957, Serial No. 606,439, August 27, 1956. Applicationfor reissue July 11, 1958, Serial No. 755,820

2 Claims. (Cl. 51-206) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

The invention relates to diamond cut-off wheels.

One object of the invention is to provide a diamond cut-off wheel oflong life. Another object is to reduce erosion of the steel center,especially adjacent the segments. Another object is to provide animproved structure for such wheels which can be easily manufactured.Another object of the invention is to provide superior metal bondeddiamond abrasive segments for the construction of cut-ofi wheels. Wheelswhich are used to slot concrete are referred to as cut-off wheels.

Other objects will be in part obvious, or in part pointed outhereinafter.

In the accompanying drawings illustrating the manu- I facture of acut-off wheel in accordance withthis invention and also the wheel madethereby,

Figure l is a partial diametral sectional view of a closed mold showingthe first step in the manufacture of the wheel,

Figure 2 is a similar sectional view showing the second step in themanufacture of a cut-off wheel,

Figure 3 is also a similar sectional view showing the third step in themanufacture of the Wheel,

Figure 4 is a plan view of the diamond abrasive, tungsten carbide ringproduced by the manufacturing steps of Figures 1, 2, and 3 on, however,a smaller scale,

Figure 5 is a plan view of a mold for the hot pressing of the segmentsmade by cutting the ring of Figure 4, on the scale of Figure 4,

Figure 6 is a sectional view taken on the line 66 of Figure 5,

Figure 7 is an isometric view of a diamond abrasivetungsten carbidesegment made in accordance with the invention, this figure being on alarger scale than Figures 1, 2, and 3.

Figure 8 is an elevation of the completed cut-01f wheel on a scalebetween that of Figures 1, 2, and 3 and that of Figure 4,

Figure 9 is an axial sectional view taken on the line 99 of Figure 8.

For the manufacture of segments such as illustrated in Figure 7 Iprovide diamond grit and tungsten carbide molding powder and preferablyalso some sintered tungsten carbide in grit sizes ranging from 40 to320. The grit size of the dimond may be anything at all, and is notcritical. For cut-off wheels it is customary to use from 16 grit size to100 grit size diamond abrasive. Neither is the concentration of thediamonds critical. It is 'pretty universal practice'to make diamondabrasive wheels and segments in three concentrations, 100, 50, and 25.In the industry 100 concentration means about 25% diamond by volume, 50concentration means about 12.5% diamond by volume, and 25 concentrationmeans about 6.25% diamond by volume. These figures are approximate,

Re. 24,576 Reissued Dec. 16, 1958 ice Tungsten carbide molding powder isa mixture of carbide powder and cobalt powder. This mixed powder isavailable on the market in grit sizes of from one of five microns.However, I can use any powder which is fines finer than 180 grit size.Furthermore, it is known that the tungsten carbide is replaced in wholeor in part by either or both of titanium carbide and tantalum carbide inmany molding powders so the carbide is selected from the groupconsisting of tungsten carbide, titanium carbide, and tantalum carbideand mixtures thereof. While nickel and iron have been proposed and to acertain extent used as the metal bond, and mixtures of all three ofthese metals have been used, cobalt is almost universally used today.The ratio, by'weight in this case of the carbide to the cobalt can beanywhere from 20% to and preferred mixtures are 40% carbide 60% cobalt,and 50% carbide 50% cobalt, and 60% carbide 40% cobalt. I

The sintered carbide cobalt grit can have a composition that goes from50% carbide, 50% cobalt to as high as carbide and5% cobalt. I have usedgrit -consisting of 94% carbide, 6% cobalt and prefer grit sizes of 80to 180. The carbide in the sintered carbide grit can be any of the threeabove mentioned and mixtures thereof.

Referring now to Figure 1 I provide a mold comprising a mold band 10 ofannular shape, a bottom plate 11, a mold center 12, an inner top moldring 13, and an outer top ring 14. The bottom plate 11 and the center 12may be secured together by a bolt 15 and a nut 16. The ring 13 hasthreaded bores 18 for the insertion of screws such as the ring bolt 20of Figure 3 to pull out th rings. The mold parts of Figure 1, as well asthose of Figure 3 may be made of steel. Assembling the mold parts ofFigure 1 all except the ring 13 leaves an annular groove 21 between thecenter 12 and the ring 14. Into this groove I spread the mixture ofsintered carbide and carbide with cobalt molding powder, well mixed. Ithen insert the ring 13 and close the mold in an hydraulic press with apressure which for example is two tons per square inch.

Removing the ring 14 which can now be done without spilling any of thesintered carbide and sintered powder with cobalt because the pressurehas made this into a fairly strong ring 25, I thereby create an annulargroove 26 into which I spread the mixture of diamond abrasive andcarbide molding powder, including the cobalt which inevery case is thereal bonding material being a soft metal which readily sinters. I thenreinsert'the ring 14 as shown in Figure 2, and again press with apressure which may be the same as for the first operation, namely twotons per square inch. Figure 2 shows the mold closed.

Referring now to Figure 3, both' of the rings 13 and 14 have beenremoved. On top of the center 12 I place a spacing plate 30 forconvenience; this is a steel' disc. I provide a further outer ring 31shaped as shown having threaded bores 32 for ring bolts 20. Figure 3shows the mold closed, with the ring 31 down but in-moving down it hasmoved the mold band 10. The mold assembly of Figure 3 is pressed in ahydraulic press with a greater pressure which usually is 50 tons to thesquare inch.

Having thus pressed the two mixtures together I open the mold of Figure3, which can be readily done using the ring bolts 20, and take out thering .40 consisting'of a diamond-carbide cobalt annulus 41 integrallymolded onto an annulus 42 of sintered carbide and carbidelwith cobaltmolding powder. This ring 40 removed from the press of Figure 3 is shownin Figure 4. I then cut the ring 40 in the green state (meaning beforesintering) into sectors 40a, Figure 7, consisting of sectors 41a moldedonto sectors 42 T e m l o Fi ure 5 comprises a r h te rise 9, graphitesegments 51, truncated graphite segments 52, notched graphite bars 53and 54, graphite spacer sectors 55 in in h c es. o e bar .5 and 4 nd raan b ocks 56 and 7. an fi tin t e h r as sh in i u e 5 a leaving pac fthe in ert n he ec rs 40a, Referring'now to Figure 6, this mold iscompleted by a graphite top plate 60 and a graphite bottom plate 61shaped to fit the sec-tors 40a which are loaded into the mold of Figures5 and 6 as shown.

The loaded-mold of Figures 5 and 6 is then taken to a hot press, notshown. This can be an induction heated hot press capable of producing apressure of about two tons per square inch upon the mold plates 60 and61. Such hot presses are regularly available and the heat is produced inthe electrically conductive material in the press by ahigh frequencymagnetic field produced by high frequency electric current in a coil ofcopper tubing through which cooling water is flowing. I then hot pressthe sec or a n r P s u o two t ns e S u e inch, the present preferredpressure which can be varied, while heating the sectors 40a to atemperature of between 1200 C. and 1300 C This range of temperature isgiven because it is difficult to determine the exact temperature of thesectors during the heat treatment and I find that by attempting to reach1250" C. very satisfactory result are achieved. When the mold of Figuresand 6 has cooled and the sectors 40a have been removed they arecompleted.

The sectors 40a are now welded to a steel center 70, Figure 8, by atechnique such as fully described in the patent of my colleague Duane E.Webster, No. 2,488,151, dated November 15, 1949. This involves the useof strips of solder which, as shown in Figure 9, becom integral junctionportions 71. The steel center 70 has radial cuts 72 therein to space thesectors 40a which has a double advantage facilitating manufacture by theprocess .of the Webster patent, and increasing the cutting ability ofthe cut-off wheel of the invention. The Webster patent mentions silversolder which I also prefer but other solders can be used. This step ofuniting the sectors 40 integrally to the steel center 70, which is adisc with the cuts 72 and central hole 74, can be called welding orsoldering or if brass is used it can be called brazing.

I have made tests comparing cut-off wheels as above described withcut-off wheels exactly the same except that they lacked the sectors 42aand instead the sectors 41a molded out of diamond-carbide and cobaltwere soldered directly to the center 70. In order to make a faircomparisonthe outside diameters of the two wheels were the same whichrequired the diameter of the center 70 for the wheel having no sectors42a to be greater than the diameter of the invention wheel by twice theradius .of a sector 42a. The mixture for the sectors 41a, and this canbe understood to be a specific example for the present disclosure, wastwenty-five concentration diamonds as previously defined, the diamondsbeing 36 grit size, with 12 weight percent sintered carbide which wasmainly tungsten carbide-and acquired from Kennam'etal Incorpolrate'dunder their brand mark K 6, with 87 /2 weight percent 50% [liquid] byweight tungsten carbide powder, 50%by weight cobalt which was alsoacquired from Kennametal with no brand mark, these percentages adding upto 100 and representing the bond component. The mixture for the sectors42a, and this is further an example for the practicing of my invention,was 12% weight percent sintered carbide, which was mostly tungstencarbide, and acquired from the Kennametal Incor porated and sold undertheir brand mark K-6, and the "grit size of the sintered carbide was 80.With this was mixed 87 /2 weight percent of 50% by weight tungstencarbide from the last named company and sold under no brand markand of 2to 3 micron size together with 50 weight percent of cobalt moldingpowder,

These two wheels thus prepared having, identical b v ec o 4 2 ant siitsrias ash is. that thi in e i615 wheel had also sectors 42a while theother one did not, were compared in a cutting test cutting newly laidconcrete such as is laid for roadways. In modern practice a concreteroadway is laid continuously without breaks. But slots are required sothat, when the concrete shrinks, it will break where desired, thusopening graps for later expansion of the concrete. The two wheels wereused on the same concrete which was what is called preset, that is tosay newly laid and not having yet fully set. This is customary practice,namely to cut the concrete which has been preset.

It will be noted that the sectors [42a] 41a are [thinner] thicker thanthe [sectors 41a] center 70. This gives an undercut structure to thewheel which provides for full clearance of the wheel in the cut. Thegeometry of the wheel having no sectors 42a was the same as theinvention wheel only at the location where the sectors 422. were in theinvention wheel there was simply steei. At the junction of the steelwith the sectors 41a in the wheel having no sectors 42a the wear inmills per feet of cut was 4.68. This corresponds to the spot mark-ed xin Figure 9 where the wear-in 100 feet cut was 1.88 mills. At the spotmarked y in Figure 9 the wear in mills per 100 feet out was only .77.The depth of cut was in all cases the same being 2% inches. The wearspots x and y and the other one on the other wheel were arcuate grooves.

Wear at the junction of steel with the sectors 41a as high as 4,68 woulddefinitely destroy the wheel before its useful abrasive life had beenexhausted. The reduction of this wear by a factor of 2 /2 gives asatisfactory life to the invention wheels. The diamond abrasivecombination of diamonds bonded with cobalt and containing carbide whichis essentially a filler gives, for the cutting of concrete, a wheel oflong life having low wheel wear and a high cutting rate. I do not havethese figures but am certain of the fact that this type of abrasivesegment is the best now known for the cutting of concrete which is nowdone on a large scale. The crux of the invention is the greatimprovement in wear at the point x and y.

It will thus be seen that there has been provided by this invention adiamond cut-off wheel in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As many possible embodiments may be made of the aboveinvention and as many changes might be made in the embodiment above setforth, it will be understood that all matter hereinbefore set forth orshown in the accompanying drawings is to be interpreted as illustrativeand not in a limiting sense.

I claim:

1. A diamond cut-off wheel consisting of a disc-shaped center slottedwith slots at and inwards from the periphery, metal bonded diamondabrasive sectors welded to the periphery, said sectors consisting of twointegral sector parts, a first sector part adjacent and welded to theperiphery of the metal center essentially consisting of particles ofcobalt bonded carbide of grit size from 80 to with carbide fines finerthan 180 all bonded to gether with cobalt, and a second sector partintegral with said first sector part and radially exterior of itessentially consisting of diamond abrasive with sintered carbideparticle of grit size smaller than 80, each said particle being carbidebonded with cobalt and cobalt bonding said sintered carbide and saiddiamond abrasive into an integral [center] sector, said second sectorhavinga width greater [than said first sector and greater] than saidcenter.

2. A diamond cut-ofi wheel consisting of a disc-shaped center slottedwith slots at and inwards from the periphery, metal bonded diamondabrasive sectors welded to the periphery, said sectors consisting of twointegral sector parts, a first sector part adjacent and welded to theperiphery of the metal center essentially consisting of diamond abrasiveand carbide particles bonded with particles of cobalt bonded carbide ofgrit size from 80 to cobalt into an integral sector, said second sectorhaving 180 with carbide fines finer than 180 all bonded together a widthgreater than said center.

with cobalt, and a second sector part integral with said first sectorpart and radially exterior of it comprising 5 No references cited

